Application of strip coating to cathode



y 1961 D. R. KERSTETTER ETAL 2,986,671

APPLICATION OF STRIP COATING T0 CATI-IODE Filed Aug. 51, 1954 INVENTORS DONALD R. KERSTETTER ERNEST S. WENNIN BY W ATTORNEY rates APPLICATION OF STRIP COATING T CATHODE Donald R. Kerstetter and Ernest S. Wennin, Emporium,

Pa., assignors, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, 'DeL, a corporation of Delaware Filed Aug. 31, 1954, Ser. No. 453,235

1 Claim. (Cl. 313-346) This invention relates to coated electrodes and to a process for coating electrodes.

Heretofore in the manufacture of coated electrodes, such as cathodes, it has been the practice either to spray coating capable of being rendered emissive on selected areas of a conductor, as in the case of manufacture of indirectly heated cathodes, or to electrophoretically deposit such a coating on an electrode, as on a heater wire, from which subsequently selected portions of the coating were stripped to provide for connection of the electrode to terminal pins. These methods did not easily lend themselves to the use of automatic machinery and did not result in uniformity of thickness of coating on the electrodes. In the case of manufacture, for example, of coated cathode sleeves, it has been the practice for anoperator to individually place the uncoated sleeves in parallel array in a rack having parallel bars. The bars were placed across the sleeves and embraced the ends thereof to mask ofi these portions from the spray subsequently applied, by the operator, to the racked cathode sleeves. In the case of electrophoretic coating, where a wire is slowly passed through a carbonate mixture, the density of the mixture varies from time to time and the resulting coating, therefore, is not uniform. Electrodes have also been made by spraying the emissive material on a rigid smooth surface such as glass, stripping the formed film from ofi the glass and applying the same to a metal component such as a spiral tantalum wire.

However, in this last method because of the thickness and rigidity of the glass it is not possible to provide a compact supply of coating material ready for transfer to other surfaces.

It is an object of this invention to provide a process which lends itself easily to automatic production and storage of coated electrodes particularly where isolated areas on an electrode are coated.

Another object of the invention is to provide a laminated structure of coating film and flexible backing of the coating and the coating support.

It is a still further object of this invention to provide 'an electrode with a uniform coating thereon and more particularly an electrode with a coating which when processed will give a uniform emission.

Yet another object of this invention is to provide a means for providing a coating method which involves the economic use of coating material and without the loss of such material as ensues where cathode sleeves or heater wire are sprayed or where attempts are made to strip a film from a rigid backing support.

Other objects will be apparent after reading the following specification -and claim in conjunction with the accompanying drawings in which:

Fig. 1 is a perspective view of a strip of laminated 2,986,671 Patented May 30, .1961

material, a layer of which is to be utilized as a coating on a cathode sleeve.

Fig. 2 is a perspective view of tabbed cathode sleeve to which the coating is to be applied.

Fig. 3 shows a laminated slip or severed section of the laminated strip with a cathode sleeve in position on it to be enwrapped by the coating layer.

Fig. 4 shows a perspective view of the completed cathode on a coating layer supporting slip just after it has been enwrapped by the coating layer.

Fig. 5 is a section through the sleeve and coating layer supporting slip.

Fig. 6 shows the enwrapped cathode by itself.

Fig. 7 shows the coating layer supporting slip by itself.

Figs. 8 and 9 are views showing the laminations pre liminary separated from each other for the purpose of carrying out a modified form of method of applying the coating to the sleeve.

Fig. 10 shows the sleeve laid on the coating preparatory to the coating being enwrapped about the sleeve.

Fig. 11 shows the carrying out of the method of this invention with a filamentary type cathode rather than a cathode sleeve.

Fig. 12 shows a completed coated filament made in accordance with this invention, and

Fig. 13 shows the coated filament in bent form ready for mounting in an electronic device.

For an explanation of how the method of this invention may be carried out, two types of cathodes have been selectedan indirectly heated cathode and a directly heated cathode, but it should be understood that the invention is not limited to the types shown but is applicable to any type of electrode selected.

In carrying out the invention there is preliminarily provided a fiat backing member which may be a highly polished thin and flexible metal, calendered paper or other like material from which a sprayed-on coating with comminuted material therein may be readily stripped as by partially curling the member at the stripping line. In a preferred form of the invention, calendered paper of the flexibility and thickness ordinarily employed as writing paper is selected. This paper may be of any size suitable, after being coated, for being cut up into slips or leaves. In the illustration, the backing member is shown as a strip of calendered paper 10 on which is a coating 12. One advantage of this species is that the laminated structure may be rolled up and stored for future use. The coating, where utilized on a cathode sleeve to form the emissive element, consists of any potentially electron emissive material, such as the carbonates of strontium, barium and calcium, held in a binder with sufiicient plasticizer therein to allow the-coating to flex without cracking. The coating may be formed in film or strip form by applying a spray to the flexible backing member. The coating material can also be brushed on, extruded, rolled or applied to the strip by many other methods common to plastic film manufacture. The nature of the coating and of the backing member is such that the backing member can be easily stripped from the coating, leaving the latter as an intact film. Best results are achieved by the use of a dual density film obtained by first coating 21 surface as described above with a preparation comprising 1250 grams co-precipitated triple carbonates 1.025 liters of binder .700 liter of Pentacetate and then spraying onto the dried film a second coating of lower density than the substrata, obtained by spraying, the second film being controlled as to its density by varying the conditions of spraying as by controlling the proportion of air to composition. Generally the second 3 coating, although less. densethan the first coating, has the same composition as the first coating.

The triple carbonates are preferably admixed in the following proportions:

Percent by weight Barium carbonate 57 L2 Strontium carbonate 38.8 Calcium carbonate 4.0

The composition of the binder may be any of the following, depending on the degree of flexibility of'binder desired:

N-amyl acetate Z-methyl butyl acetate 3-methyl butyl acetate 4-methyl butylacetate 3-ethyl propyl acetate Afterthe laminated fabric has been formed, it may be cut up into strips such as the strip 14 shown in Fig. 1 and then cut into slips or. leaves. 16 by, slitting the, strip as at 18. The coating 12 on the slip is to be adhered to a cathode member such as the circular cathode sleeve 20 shown inv Fig. 2, although, as will be later apparent, a rectangular or other shaped sleeve will work as well. The sleeve is a conventional element in the electron tube art and is here shown as comprising a nickel tube with extruded bead 22 to locate the cathode in an insulating wafer and a tab member 24 to be utilized to electrically connect the cathode sleeve to a tube terminal. The width ofthe slip. is made so as to equal or be just slightly less than the circumference of the tubular cathode sleeve and thelength of the slip is made so as to cover the desired height of the cathode sleeve. The slip if desired can be cut-to the size and shape of a flat cathode face as a cathode, button in an electron tube.

The coating may be made to adhere to the cathode in the following fashion:

The cathode sleeve 20 is wet-ted in a solution which will partially dissolve the coating binder. In the case where the-binder is nitrocellulose, the solvent employed may be Pentacetate. The cathode is then laid along the longitudinal medial axis of the slip in a position such that the proper length of sleeve would extend at each end from thecoated portion of the cathode. Upon contact of the wetted sleeve with the film 12 both side portions of the ends will leave the backing and quickly wrap themselves around the sleeve to form the cathode of Fig. 4.

4 It appears that the solvent has an immediate suflicient liquifying effect upon the binder in the film such that the surface tension ensuing causes the wrapping action to take place. In the case of a planar surface, contact at one point between film and surface ensures adherence of the entire surface and film.

In another mode of operation, see Figs. 8 to 10, the' film 12 is first stripped from the backing member 10, as by using a thin blade, bending back the backing member 10 as needed to facilitate the operation and the sleeve 20 with Pentacetate applied thereto is placed on the film 12, to be enwrapped by the film. In still another mode of operation, the sleeve 20 is laid, dry, on the film ll and solvent liquid is applied to the film immediately adjacent the sleeve thereby effecting wrapping of the film about the sleeve, the solvent apparently spreading around the cathode sleeve in advance of the wrap as it envelops the sleeve. The speed of the wrap is very rapid, approaching the order where it is hard to follow the action with the eye, but may be'made less rapidby selecting a less active solvent or a less su'sceptible-tb-solutio'n binder in the film. i

As another example of the invention, attention isv directed to Figs. 11 to 12. Here a flat ribbon or tape of heater wire'30 is laid across two isolated slips 32, 34 of film of a composition such as had been'described before, and the solvent is applied, as' before, to cause the two slips to wrap themselves in spaced relation, about the heater tape. Subsequently the heater tape is bent to suitable form, as shown in Fig. 13 to be utilized as a die rec'tly' heated cathode in an electron device. Obviously the 'wire'30 may be of channel cross section without any ch'ange in operation.

'The advantage of using the flexible backingmember is not only in the capability of-making a roll of the laminated fabric for storage and in permitting easy stripping of film from slips, but also in'enabling, in automatic machinery, the laminated roll to be unrolled-with the film stripped off-and fed in a plane to a cutting. equipment while the backing member itself is bentv back and fed onto a take-up roll.

Having'thus described the invention, what is claimed as new is:

An electrode comprising a metal cathode base and. a strip of material surrounding the metal, the strip itself being quadrilateral with rectangular corners, self supporting prior to the application ofthe strip to the base and composed solely of potentially electron emissivematerial held within a flexible binder, the strip on thecathode base'having opposing edges in abutting relationship.

References Cited-in the file ofthis patent UNITED STATES PATENTS 

